1. Field of the Invention
This invention relates to heat exchangers generally, and, more particularly, to heat exchange processes and to heat exchangers that contain and utilize fluidized small solid particles to improve the transfer of heat on one side of the wall that separates two fluids.
2. Background Art
High heat transfer rates have been reported for surfaces immersed in small solid particles that are suspended and kept in motion by an upward flow of a fluid. The overall heat transmission coefficient of a heat exchanger is in the range from 35 to 50 BTU/hrxc2x0 F.ft2 (i.e. British thermal unit per hour-degree Fahrenheit-square foot). Details of the heat exchanger are described in my pending U.S. patent application Ser. No. 09/028,053 filed on Feb. 23, 1998. The heat exchanger includes a fluidized bed of small solid particles that are suspended in a flow of a fluid in which the downward tendency of the small solid particles to fall by gravity is equaled by the upward drag force of the fluid flow. The heat exchanger includes a plurality of flat surfaced pipes or tubes, a top woven wire mesh or perforated sheet disposed on top surfaces of the flat surfaced pipes, and a grid plate disposed on bottoms of the flat surfaced pipes. The small solid particles are disposed between the flat surfaced pipes and between the top woven wire mesh and the grid plate. This heat exchanger, however, needs additional new features for the top woven wire mesh or perforated sheet and the grid plate to make the heat exchanger more efficient.
It is an object of the present invention to provide an improved heat exchanger exhibiting increased efficiency.
It is another object to provide a heat exchanger that maintains the same capacity although constructed smaller in size.
It is still another object to provide a heat exchanger having folded and shaped woven wire mesh or perforated sheets able to reduce the overall pressure drop within the heat exchanger during operational service.
It is yet another object to provide an improved orifice plate equipped with a plurality of orifices allowing fluid passage.
It is a further object to provide a heat exchanger having a more efficient fluidized bed.
It is also an object to provide a heat exchanger able to improve heat exchange rates by using small solid particles having tetrahedron or pyramid shapes.
These and other objects may be achieved with a heat exchanger that contains solid particles in a fluidized bed inside the heat exchanger, that has heat transfer surfaces that are not immersed in the solid particles, that has a loosely packed fluidized bed of small solid particles, that generally only allows a bubbling boiling movement of the solid particles direction rather than allowing a circulating motion, that does not need to use devices to restrain the fluidized bed, does not require any special coating on the heat exchanger surface, that has no vertical tubes, that maintains the two fluids exchanging beat separate from each other, does not require using heating elements in the fluidized bed, that uses flat walls to increase the heat transfer coefficient, that does not use slits or slots, that does not have a space between the distributor plate and the bottom of the tube inlets that creates circulating fluid patterns, that does not require embedding larger particles in the fluidized bed, and uses small solid particles with shapes that allow for an increased amount of heat exchange. This should allow heat exchangers of all types to be made smaller than priorly possible while still maintaining the same level of heat transfer between the two fluids.
The heat exchanger includes flat surfaced pipes or tubes conveying one of the fluids involved horizontally. The flat surfaced pipes are spaced-apart from each other and firmly attached to a grid plate that is perforated with orifices that introduce the other fluid involved in the heat exchange process and flowing upward and between the flat surface pipes. A top woven wire mesh or perforated sheet is held tightly against the tops of the flattened pipe or tubes to keep the small solid particles from falling out from a top portion of the heat exchangers between the tops of the flattened pipe when the heat exchangers are handled. The bottom woven wire mesh or perforated sheet is held tightly against the bottom or inlet side of the grid plate to keep the small solid particles from draining out from a bottom portion of the heat exchanger between the bottoms of the flattened pipe whenever the heat exchanger has no upward flowing fluid through the orifices. The small solid particles are disposed to move within a heat exchanging space defined between the flat surfaced pipes and between the top woven wire mesh or perforated sheet and the bottom woven wire mesh or perforated sheet. Bubbles are formed above the orifices whenever more fluid is introduced through the orifices than will pass through the spaces between the small solid particles.
The woven wire mesh or perforated sheets on the top and bottom can be folded or shaped to both increase their respective surface areas and decrease the volume of the heat exchanging space which will thereby reduce the overall pressure drop when in service. Some versions of the improved heat exchangers may be constructed without any orifice plate. The orifice plate may contain one or more orifices in a given enclosed area. The orifices may be round, square or of some other shape. Tetrahedron or pyramid shaped particles may be used for the small solid particles to be manufactured.